Disulfonylamine alkali metal salts are compounds that are useful as electrolytes for secondary cells or as additives for adding to electrolytes of secondary cells (Patent Document 1). Further, it is known that reducing the amount of impurities within the electrolyte of a secondary cell has a favorable effect on the discharge capacity and the current efficiency of charging and discharging the secondary cell (Non-Patent Document 1). Accordingly, the development of methods for producing disulfonylamine alkali metal salts with high purity are currently being pursued.
For example, Patent Document 2 proposes a method for producing a high-purity disulfonylamine salt in which following the fluorination reaction of bis(chlorosulfonyl)amine, the reaction solution is brought into contact with an aqueous alkaline solution in order to remove impurities.
Patent Document 3 proposes a method for producing a disulfonylamine alkali metal salt which includes a step of concentrating a solution of the disulfonylamine alkali metal salt while bubbling a gas through the reaction solution that contains the disulfonylamine alkali metal salt, and/or a step of concentrating a solution of the disulfonylamine alkali metal salt by thin-film distillation.
Patent Document 4 proposes a method for producing a bis(fluorosulfonyl)amine alkali metal salt by reacting a bis(chlorosulfonyl)amine ammonium salt with hydrogen fluoride to obtain a bis(fluorosulfonyl)amine ammonium salt, and then reacting an alkali metal compound or the like with the obtained bis(fluorosulfonyl)amine ammonium salt.